1. Field of the Invention
The present invention relates to a plate rolling mill. More particularly, the invention relates to a rolling mill including a grinder installed in a rolling stand to grind the surface of each of working rolls, and a rolling method, the rolling mill being suited for rolling a plate requiring good quality, especially a metal plate, and the working rolls being movable in axial directions.
2. Description of the Related Art
In the field of plate rolling, there has been a demand for a plate quality improvement. The profile of a working roll surface has been improved in an effort to increase the accuracy of plate dimensions, and various types of rolling mills have been developed. For example, Conventional Technology 1 (JP-B-51-7635) discloses a 4-high rolling mill having working rolls and reinforcing rolls provided in its rolling stand. The working rolls are movable in axial directions, and working rolls bender is installed. According to the Conventional Technology 1, the controllability of plate thickness distribution can be improved by changing an axial position of each of the working rolls, and by using the working roll bender in combination. In addition, according to the Conventional Technology 1, by changing the axial position of the working roll, the surface region of the working roll brought into contact with a plate is changed in the axial direction, the wear of the working roll surface being uniformed, and local uneven wear is minimized. Thus, there is obtained an advantage in manufacturing cost because of a prolonged time of using the working roll. Moreover, according to the Conventional Technology 1, a thermal crown and a wear crown occurring on the working roll surface are cancelled each other, and a coffin type limitation hitherto occurring regarding the plate width order of a rolling schedule is relaxed. Thus, it is possible to make a rolling schedule more freely. For the foregoing reasons, the Conventional Technology 1 has been widely accepted in a plate manufacturing field, and still used.
Another Conventional Technology 2 (JP-B-2708351) discloses a rolling mill including an on-line roll grinder. According to the Conventional Technology 2, a grindstone brought into contact with a working roll is formed to have a highly elastic thin disk-like structure, so that the effect of whirling caused by the vibration of the working roll or the eccentricity of a shaft center line is absorbed for good grinding, whereby even in an actual rolling mill, stable grinding is performed. In addition, according to the Conventional Technology 2, there is provided such a function as to detect a profile of the working roll while pressure-contacting the grindstone onto the surface of the working roll with a constant force so that the movement of the grindstone may be detected to thereby obtain irregularity on the working roll surface. Thus, it is possible to grind in an on-line manner each of the working rolls by detecting the profile of the working roll. In the Conventional Technology 2, a period of time for using the working roll can be further prolonged by performing grinding during the rolling. As in the case of the Conventional Technology 1, it becomes possible to obtain a considerably free rolling schedule, and the rolling mill has been used in the plate manufacturing field.
Still another Conventional Technology 3 (JP-A-61-296910) discloses a method of making a wide wear profile by using both of roll-shifting and grinding a roll surface region of each of the working rolls which region is located outside of a plate to be rolled (, which grinding is referred to as xe2x80x9cplate-outside-grindingxe2x80x9d hereinafter). According to the Conventional Technology 3, as in the case of the Conventional Technology 1, since the changing of the axial position of the working roll makes the uniform wear on the working roll surface and minimize local uneven wear, there is such an advantage to make the manufacturing cost low because of a prolonged period of time regarding the use of the working rolls. Moreover, a working roll region located outside a plate width is ground by an amount equal to the amount of working roll center wear so that the abrupt change of the wear profile may occur outside of the plate width. Thus, any contact is prevented from occurring between the plate to be rolled and the working roll region having a considerably changed wear profile. In this way, since the transfer of the abruptly changed wear profile portion of the working roll to the plate is prevented, the influence of the wear profile of the working roll surface on the plate to be rolled is deemed to become small.
However, in any of the foregoing Conventional Technologies 1 to 3, no specific means has been disclosed from the viewpoint of keeping a good profile of the working roll surface over the whole of rolling cycles in order to prevent the defects of a plate surface from occurring which defects are considered to be the problem of plate quality. As the result of the researches of the inventors of the invention, the inventors discovered that when rolling was performed by any one of the Conventional Technologies 1 to 3, deterioration of plate quality occurred with the progress of rolling, making it difficult to perform many times of plate-rolling. This problem will now be explained while referring to the drawings.
FIGS. 2A and 2B illustrate working roll surface profiles and thermal expansion and wear profiles which constitute the working roll surface profile, in a case where plates equal in width are subjected to hot rolling by using a rolling mill having no working roll shifting. The working roll surface profiles shown in FIGS. 2A and 2B indicate change per roll radius. In the case of usual rolling of a plate, a temperature of plate end portions are lower than that of a plate center, and plate surface scales and hardness are different between the plate center and the plate end portions. The wear amount of a working roll region brought into contact with each of the plate end portions is larger than that of another working roll region brought into contact with the plate center (larger by 1.05 to 1.25 times than center wear). In other words, working roll wear takes a peak shape at the working roll end region. The thermal expansion profile of the working roll surface becomes a constant, gently-sloping profile saturated after the rolling of 40 or more pieces of rolled plates. Accordingly, as shown, the working roll surface profile constituted by the wear and thermal expansion profiles receives the great influence of the shape of the end portion peak wear, and is suddenly changed near the plate end portions. When such a suddenly changed working roll region is brought into contact with and transferred to the plate, flaws or defects occur on the plate surface. Thus, the contact of this region with the plate must be avoided. For this reason, there has been used such a so-called xe2x80x9ccoffin schedulexe2x80x9d of rolling as the rolling is performed by a process having the steps of: sequentially changing plate widths so that the width of each of the plates to be rolled is increased sequentially till such a period of time of small wear as to correspond to about 10 to 20 pieces of rolled plates to thereby make the thermal expansion profile dispersed; and then changing the plate width so that the width of each of the plates to be rolled becomes narrow sequentially to prevent the working roll end regions having the peaks of the wear profile from contacting with the plates.
FIGS. 3A and 3B illustrate working roll surface profiles and thermal expansion and wear profiles which constitute each of the working roll surface profiles, in a case where the working roll shifting of the Conventional Technology 1 is performed and plates equal in width are subjected to hot rolling. Each of the working roll surface profiles shown in the drawings indicates a change per roll radius. In the case of the profiles, the working roll is moved 10 mm axially every two pieces of rolled plates, and a maximum moving position is xc2x1100 mm. It can be understood from the drawings that the shape of the peak wear of the working roll end regions occurring in the case of no working roll shifting disappears. The working roll surface profile corresponding to 44 pieces of rolled plates takes a gentle-sloping shape and, since the wear profile and the thermal expansion profile are cancelled each other, the surface profile also becomes smaller in value. As this working roll surface profile is for one working roll and upper and lower working rolls are located in point symmetry to the place center, the profile of roll gaps symmetrical left and right is transferred to the plate. By making effective use of this, the limitation occurring regarding the plate width order of the coffin schedule type is relaxed, making it possible to make a considerably free rolling schedule. However, a period of time regarding this advantage is short and, if rolling further proceeds, the wear profile like the that of 160 pieces of rolled plates shown in FIG. 3B becomes predominant, resulting in a working roll surface profile having the great change near the plate end portions. This is attributed to the fact that, although the growth of the thermal expansion profile is saturated by about 40 pieces of rolled plates, wear is increased in proportion to the number of pieces of rolled plates and the wear profile is also enlarged in unlimited manner. Therefore, strictly speaking, the range of the number of rolled plates in which the wear and thermal expansion profiles can be cancelled each other is extremely narrow. In other words, even in a case of using the working roll shifting, wear becomes large after a certain number of rolled plates with the result that the plate profile is deteriorated, and thus the working rolls must be changed before the deterioration. It can therefore be said that the use of the Conventional Technology 1 brings about the cancellation effect of the wear and thermal expansion profiles, but this effect terminates in a short period of time. Further, since the wear is increased in proportion to the number of rolled plates, it can be said that the number of rolled plates obtained by the same working roll is not increased so much.
FIGS. 4A to 4C illustrate working roll surface profiles when rolling is performed by using the on-line roll grinder of the Conventional Technology 2. The working roll surface profile shown in the drawing indicates a change per roll radius. If no working roll shifting is performed as in the case described above with reference to FIGS. 2A and 2B, the wear profile of a working roll takes the shape of peak wear in each end portion. The peak wear must be removed to relax the limitation of the coffin schedule, and the case of grinding the whole working roll region located outside a plate width down to a peak depth is assumed herein. In this case, because of the grinding of the whole working roll region located outside the plate width to the peak depth, a surface profile becomes gentle-sloping having no peak wear in any case of the 42 and 160 pieces of rolled plates. However, as apparent from the deformation amount of a working roll center region, wear and thermal expansion profiles of the working roll surface corresponding to the inside of the plate width act not to be cancelled each other but to be added to each other to make the working roll surface profile large in value, and there is no cancellation effect between the wear and thermal expansion profiles, causing the surface profile to be larger in values than the thermal expansion profile. If rolling is further continued, the wear profile having a peak in the working roll region corresponding to the inside of the plate width becomes large, leading to further enlargement of the working roll surface profile, and this enlargement develops to an unlimited extent. Since the amount of grinding corresponds to the amount of the peak wear, the depth of the grinding is necessary to be larger by 1.05 to 1.25 times than that in the case of no peak wear influence. Thus, by using the Conventional Technology 2, the surface profile becomes gentle-sloping, and it lasts for a long period of time. However, it is pointed out that there is no cancellation effect between the wear and thermal expansion profiles, and the increasing of the value of the working roll surface profile proceeds. In addition, the amount of roll grinding must be set deep, and cost performance regarding the use of rolls is not so advantageous.
FIGS. 5A to 5C illustrate working roll surface profiles in a case of rolling performed while making a wide wear profile by using in combination the working roll shifting and the xe2x80x9cplate-outside-grindingxe2x80x9d of the working roll in the Conventional Technology 3. The working roll surface profile shown in the drawing indicates a change per roll radius. As described above with reference to FIG. 3, according to the Conventional Technology 3, the working roll shifting removes the shape of peak wear in the end portion, and the grinding of the working roll end region located outside the plate width down to the amount of the working roll wear depth corresponding to the plate center for each rolling makes the working roll surface profile almost equivalent to the thermal expansion profile of the working roll. Accordingly, the surface profile becomes a gentle-sloping profile in any of the 42 and 160 pieces of rolled plates. However, as apparent from the amount of a roll center surface deformation shown in FIG. 5C, there is no cancellation effect between the wear and thermal expansion profiles, and the surface profile is large which corresponds directly to the value of the thermal expansion profile. It is apparent that by using the Conventional Technology 3, the surface profile becomes gentle-sloping and it lasts long, but there is not any cancellation effect at all between the wear and thermal expansion profiles, and the working roll surface profile becomes large. Thus, as a technical problem, there occurs the improper profile on the working roll surface, which becomes a problem when rolling is performed by using the working rolls. The deterioration of the working roll surface profile causes uneven plate thickness distribution, the deterioration of plate quality and other disadvantages, resulting in the difficulty of stable rolling of good-quality plates.
An object of the invention is to provide a rolling mill of a type having in a rolling stand a grinder for grinding the surface of a working roll movable in an axial direction, which rolling mill is capable of providing a uniform plate thickness distribution and manufacturing a good-quality plate.
Another object of the invention is to provide a rolling method capable of providing a uniform plate thickness distribution and manufacturing a good-quality plate.
According to the first aspect of the invention, there is provided a rolling mill comprising at least one pair of upper and lower working rolls each movable in a direction of axis of each of said rolls, at least one of profile-measuring means for measuring a profile of said working rolls and profile-estimating means for estimating said profile of said working rolls, grinding means for grinding a surface of said working rolls, and grinding-instructing means for instructing the grinding means to perform grinding of the working rolls when at least one of a value of measured profile of said working rolls and another value of estimated profile of said working rolls reaches a given value.
According to the second aspect of the invention, there is provided a rolling mill for producing a plate, comprising a rolling stand, at least one pair of upper and lower working rolls provided in said rolling stand and movable in a direction toward a driving side of said rolling mill or in another direction reverse to the former direction each of which working rolls is moved in a direction reverse to each other, and working rolls-grinding means for grinding a working roll surface region located outside of a width of said plate which portion is to be in pressure-contact with the plate during succeeding rolling operations performed thereafter by axial movement of said working rolls, or for grinding another region further including more outside working roll region than the former working roll region, or for grinding a whole working roll surface region located outside of said width of said plate, so that a wear profile of each of said working rolls has a suppressed growing rate of depth of wear occurring in the working rolls during rolling or so that said wear profile has a constant depth of said wear.
According to the third aspect of the invention, there is provided a rolling mill for producing a plate, comprising a rolling stand, at least one pair of upper and lower working rolls provided in said rolling stand which working rolls are movable in the direction of axis of said working rolls, grinding means provided in the rolling stand which grinding means grinds a surface of said working rolls, means for storing and calculating a cumulative number of pieces of rolled plate produced or amount of rolling performed in a period of time continuing from initial use of said working rolls, and grinding-instructing means for instructing the grinding means to perform grinding of the working rolls when said number of piece of said rolled plate or the amount of said rolling reaches a given value.
According to the fourth aspect of the invention, there is provided a method of rolling by use of a rolling mill comprising at least one pair of upper and lower working rolls each movable in a direction of axis of each of said rolls, at least one of profile-measuring means for measuring a profile of said working rolls and profile-estimating means for estimating said profile of said working rolls, and grinding means for grinding a surface of said working rolls, said method comprising the steps of comparing a given value with at least one of a measurement value obtained by said profile-measuring means and an estimated value obtained by said profile-estimating means, and instructing said grinding means to perform grinding of the working rolls when said at least one exceeds said given value.
According to the fifth aspect of the invention, there is provided a method of rolling a plate by use of a rolling mill comprising a rolling stand, at least one pair of upper and lower working rolls provided in said rolling stand and movable in a direction toward a driving side of said rolling mill or in another direction reverse to the former direction each of which working rolls is moved in a direction reverse to each other, and working rolls-grinding means for grinding a working roll, said method comprising the steps of
measuring or estimating a depth of wear of said working rolls,
performing, when said measured or estimated depth of the wear of said working roll reaches a given value,
grinding a working roll surface region located outside of a width of said plate which region is to be in pressure-contact with the plate during succeeding rolling operations performed thereafter because of axial movement of said working rolls, or grinding another region including a more outside working roll region than the former working roll region, or grinding a whole working roll surface region located outside of said width of said plate, so that a wear profile of each of said working rolls has a suppressed growing rate of depth of wear occurring in the working rolls during rolling or so that said wear profile has a constant depth of said wear.
According to the sixth aspect of the invention, there is provided a rolling method for rolling a plate by a rolling mill having at least a pair of upper and lower working rolls in a rolling stand, comprising the steps of:
moving the working rolls in axial directions;
grinding a surface of each of the working rolls by a grinder;
calculating the number of pieces of rolled plate or a rolling amount by a storing and calculating means; and
commencing grinding of each of the working rolls when the number of pieces of the rolled plate produced or the amount of rolling performed after replacement of the working roll reaches a given value predetermined on the basis of calculation or previously obtained data based on actual values.